Monitoring and Controlling Energy Delivery of an Electrosurgical Device

ABSTRACT

A method is disclosed for delivering energy to a region of tissue within a patient&#39;s body using a medical treatment system. The medical treatment system comprises an energy delivery device coupled to an energy source and the method includes steps of delivering energy, measuring an energy delivery parameter, determining distance of the energy delivery device from a conductive object and optionally adjusting a position of the energy delivery device based on the determined distance.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/410,868, filed on Mar. 2, 2012, which is a continuation-in-part ofU.S. application Ser. No. 13/286,041, filed on Oct. 31, 2011, now U.S.Pat. No. 8,623,005, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/905,448, filed on Oct. 1, 2007, now U.S. Pat.No. 8,048,071.

U.S. application Ser. No. 13/410,868 and U.S. application Ser. No.13/286,041, further claim the benefit of U.S. provisional applicationNo. 61/448,578, filed on 2 Mar., 2011. U.S. patent application Ser. No.11/905,448 further claims the benefit of U.S. provisional patentapplication No. 60/827,466 filed on 29 Sep. 2006. All of these US patentapplications and provisional patent applications are hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

The disclosure relates to systems and methods for monitoring andcontrolling energy delivery of an electrosurgical device. Morespecifically, the disclosure relates to systems and methods formonitoring and controlling delivery of energy to a region of tissuewithin a patient's body, using an electrosurgical device.

BACKGROUND OF THE ART

U.S. Pat. No. 7,651,492 granted to Wham discloses a system and methodfor performing electrosurgical procedures. The system includes sensorcircuitry adapted to measure impedance and to obtain one or moremeasured impedance signals. The sensor circuitry is further adapted togenerate one or more arc detection signals upon detecting an arcingcondition. This is accomplished by passing the measured impedance tissuesignal through a high pass filter and then passing the absolute value ofthe high pass filter through a low pass filter. The resulting filteredsignal is the arc detection signal that is scaled and capped. The systemdisclosed by Wham further includes a controller adapted to generate oneor more target control signals as a function of the measured impedancesignals and to adjust the output of the electrosurgical generator basedon the arc detection signal. Wham discloses detecting arcing bymonitoring for rapidly repeating changes in measured signal such as theimpedance signal and generating an arc detection signal. Since thesystem as disclosed by Wham relies on measuring changes in the impedancesignal, it will result in the detection of an arcing condition andcontrolling of the output even if the arcing is insignificant.Furthermore, the system may not respond even if the arcing issignificant as long as repeated arcing is not observed. Thus, Wham'ssystem includes several deficiencies with respect to arc detection andenergy control.

SUMMARY OF THE DISCLOSURE

In an embodiment of the present invention, a method is disclosed fordelivering energy to a region of tissue within a patient's body using amedical treatment system, the medical treatment system comprising amedical device coupled to an energy delivery source, the methodcomprising the steps of: (1) delivering energy from the medical device;(2) advancing the medical device while delivering energy; (3) measuringan energy delivery parameter while energy is being delivered; (4)detecting if a value of the energy delivery parameter crosses athreshold; (5) if the threshold is crossed thereby indicating proximityof the device to a conductive object, determining the relative distancebetween the medical device and the conductive object based on one ormore detected values of the energy delivery parameter; (6) determiningif the distance between the medical device and metal object isdecreasing; and (7) upon determining that the distance between themedical device and the conductive object is decreasing, adjusting aposition of the medical device and repeating steps (3)-(7) until themedical device is positioned at a desired distance from the conductiveobject.

As a feature of this broad aspect, the step of adjusting a position ofthe medical device comprises moving the medical device away from theconductive object until the value of the energy delivery parameter nolonger exceeds the threshold.

As another feature of this broad aspect, the conductive object comprisesa secondary medical device and wherein the step of adjusting a positionof the medical device comprises moving the medical device towards thesecondary medical device until the medical device is positioned adjacentthe secondary medical device. In one such example the secondary medicaldevice is selected from the group consisting of a medical guidewire anda snare.

As a feature of this broad aspect, the threshold value is equal to apre-determined value of the energy delivery parameter. As anotherfeature of this broad aspect, the energy delivery parameter is current.In one such example, the threshold value is equal to less than about 1.0Amps. In one specific example, the threshold value is equal to about 0.3Amps.

As still another feature of this broad aspect, the threshold value isequal to a base value, wherein the method further comprises a step ofdetermining the base value by measuring the energy delivery parameterupon advancing the medical device to the target site within thepatient's body.

In accordance with one embodiment of the present invention, the methodfurther comprises a step of imaging the medical device wherein the stepsof advancing the medical device and measuring the base value areperformed concurrently with the step of imaging the medical device. Inanother embodiment, the method further comprises a step of imaging themedical device wherein the step of adjusting a position of the medicaldevice is performed concurrently with the step of imaging the medicaldevice. In some such examples, the step of imaging the medical device isperformed using an imaging modality selected from the group consistingof: fluoroscopy, magnetic resonance imaging, computerized tomographyscan, electro-anatomical mapping and magnetic positioning system.

As another feature of this broad aspect, the method additionallycomprises a step of providing an indication/feedback to the user if thedistance between the medical device and the conductive object isdetermined to be decreasing. As an example of this feature, theindication/feedback is selected from the group consisting of a visualindication, an electrical control signal and an acoustic indication. Ina specific example, the acoustic indication is selected from the groupconsisting of a volume based acoustic indication and a frequency basedacoustic indication.

As still another feature of the broad aspect, the step of adjusting aposition of the medical device is performed automatically. In onespecific example, the step of adjusting a position of the medical deviceis performed automatically using an automated navigation system. In somesuch examples, the step of providing an indication/feedback to the usercomprises providing an electrical control signal that is receivable bythe automated navigation system.

In an alternative embodiment of the present invention, a method isdisclosed for delivering energy to a region of tissue within a patient'sbody using a medical treatment system, the medical treatment systemcomprising a medical device coupled to an energy delivery source, themethod comprising the steps of: (1) delivering energy from the medicaldevice; (2) advancing the medical device while delivering energy; (3)measuring an energy delivery parameter while energy is being delivered;(4) detecting if a value of the energy delivery parameter crosses athreshold; (5) if the threshold is crossed thereby indicating proximityof the device to a conductive object, determining the relative distancebetween the medical device and the conductive object based on one ormore detected values of the energy delivery parameter; (6) determiningif the distance between the medical device and metal object isincreasing; and (7) upon determining that the distance between themedical device and the conductive object is increasing, adjusting aposition of the medical device and repeating steps (3)-(7) until themedical device is positioned at a desired distance from the conductiveobject.

As another feature of this broad aspect, the method additionallycomprises a step of providing an indication/feedback to the user if thedistance between the medical device and the conductive object isdetermined to be increasing.

In accordance with another embodiment of the present invention, a methodis disclosed for delivering energy to a region of tissue within apatient's body using a medical treatment system, the medical treatmentsystem comprising a medical device coupled to an energy delivery source,the method comprising: (1) delivering energy from a medical device tomaterial within a patient's body; (2) measuring an energy deliveryparameter while the energy is being delivered; (3) detecting at leastone error if one or more values of the energy delivery parameter cross apre-determined threshold; (4) upon detection of at least one error,assessing an extent of the at least one error to determine whether themedical device is sufficiently distanced from a conductive object toallow for safe delivery of the energy to the material within thepatient's body; and (5) if the medical device is determined to not besufficiently distanced from the conductive object, adjusting a positionof the medical device and repeating steps (2)-(4) until the medicaldevice is sufficiently distanced from the conductive object.

As a feature of this broad aspect, the energy delivery parameter isselected from the group consisting of: current, voltage, phase,frequency and impedance.

As another feature of this broad aspect, the step of assessing an extentof the at least one error comprises quantifying the number of times theenergy delivery parameter crosses the threshold.

As another feature of this broad aspect, the step of determiningassessing an extent of the at least one error comprises determining if acollective magnitude of the one or more values of the energy deliveryparameter exceeds a sensitivity threshold over a predetermined timeperiod. As an example of this feature, the sensitivity threshold isfixed. As another feature of this example the sensitivity threshold isvariable/adjustable;

As another feature of this broad aspect, the step of assessing an extentof the at least one error comprises determining if a duration of timeover which the energy delivery parameter exceeds the threshold.

As a feature of this broad aspect, the medical device is selected fromthe group consisting of a radiofrequency (RF) cutting device and aradiofrequency (RF) ablation device. In one such example, an RF cuttingdevice may have a frequency that is greater than about 500 kHz. In someexamples, the RF cutting device may have a radio wave frequency that isbetween about 30 kHz to about 300 GHz.

In accordance with another embodiment of the present invention, a methodis disclosed for delivering energy within a region of tissue within apatient's body using a medical treatment system, the medical treatmentsystem comprising a medical device coupled to an energy delivery source.The method comprises the steps of: (1) delivering energy from themedical device to a material within a patient's body; (2) measuringreturn current while energy is being delivered; (3) detecting (one ormore over-currents) if the return current exceeds a threshold; (4) ifthe threshold is exceeded, assessing the extent (of the one or moreover-currents) by which the return current exceeds the threshold todetermine if the medical device is sufficiently distanced from aconductive object; and (5) if the medical device is determined to not besufficiently distanced from the conductive object, adjusting a positionof the medical device and repeating steps (2)-(4) until the medicaldevice is sufficiently distanced from the conductive object.

In accordance with an embodiment of the present invention, a method isdisclosed for delivering energy within a region of tissue within apatient's body. The method helps avoid significant arcing while stillallowing use of an energy delivery device in the vicinity of anelectrically conductive object such as a metallic object. An energydelivery parameter is monitored during the delivery of energy. The valueof the energy delivery parameter is compared to a predeterminedmagnitude threshold to determine if the value exceeds or falls below thepredetermined threshold to ascertain if there is significant arcing. Theenergy delivery is then controlled based on the extent of the arcingobserved.

In one broad aspect, embodiments of the present invention comprise amethod and medical treatment system for delivering energy to a region oftissue within a patient's body. The medical treatment system comprisesan energy delivery device coupled to an energy source. In one particularembodiment, the method comprises the steps of: delivering energy throughsaid energy delivery device; monitoring a current output of said energydelivery device; detecting one or more over-currents if the currentoutput exceeds a predetermined magnitude threshold; determining anextent of the over-currents detected over a predetermined time period;and controlling the delivery of energy based on the extent of theover-currents detected.

In another broad aspect, embodiments of the present invention comprise amethod and medical treatment system for delivering energy to a region oftissue within a patient's body. The medical treatment system comprisesan energy delivery device coupled to an energy source. In one particularembodiment, the method comprises the steps of: delivering energy throughsaid energy delivery device (which may be positioned within thepatient's body); monitoring an energy delivery parameter (for example anelectrical parameter) associated with the delivery of energy by themedical treatment system; detecting one or more errors if one or morevalues of the energy delivery parameter exceed a predetermined magnitudethreshold; determining or assessing an extent of the errors detected;and controlling the delivery of energy if the extent of the errorsdetected exceeds a sensitivity threshold over a predetermined timeperiod.

As a feature of this broad aspect, the step of determining the extent ofthe errors comprises a step of determining the number of errorsdetected.

As another feature of this broad aspect, the step of determining theextent of the errors comprises a step of determining the magnitude ofthe one or more values of the energy delivery parameter that exceed thepredetermined threshold.

As another feature of this broad aspect, the step of determining theextent of the errors comprises a step of determining the duration oftime during which the one or more errors are detected.

As another feature of this broad aspect, the energy delivery parameteris selected from the group consisting of: current, voltage, impedanceand power.

As a feature of this broad aspect, the energy delivery device is an RF(radiofrequency) cutting device.

As an alternate feature of this broad aspect, the energy delivery deviceis an RF (radiofrequency) ablation device.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, embodiments ofthe invention are illustrated by way of examples in the accompanyingdrawings, in which:

FIG. 1 a is an illustration of a medical treatment system in accordancewith an embodiment of the present invention;

FIG. 1 b is an illustration of a medical treatment system in accordancewith an alternate embodiment of the present invention;

FIG. 2 illustrates a block diagram of a fault detection circuit inaccordance with an embodiment of the present invention;

FIG. 3 illustrates a block diagram of a fault detection circuit inaccordance with an alternate embodiment of the present invention;

FIG. 4 a illustrates a circuit diagram of a fault detection circuit inaccordance with an embodiment of the present invention;

FIG. 4 b is a flow chart showing a method in accordance with anembodiment of the present invention;

FIG. 5 a illustrates a block diagram of an energy delivery system inaccordance with an embodiment of the present invention;

FIG. 5 b illustrates a block diagram of an energy delivery system inaccordance with an alternate embodiment of the present invention;

FIG. 6 a illustration of a method and system in accordance with anembodiment of the present invention;

FIG. 6 b is an illustration of a flowchart showing a method inaccordance with an embodiment of the present invention;

FIGS. 7 a-7 d are an illustration of a method in accordance with anembodiment of the present invention;

FIG. 8 is an illustration of mapping between current and distance inaccordance with an embodiment of a method of the present invention; and

FIG. 9 is an illustration of a stent and a medical device as well asrelative current values with respect to distance, in accordance with anembodiment of a method of the present invention.

DETAILED DESCRIPTION

In some medical applications, a radio-frequency medical device may berequired in order to treat an area of tissue within a patient's body.The radiofrequency device may be used, for example, to either perforatethrough a region of tissue to create a pathway through a region oftissue or to ablate a region of tissue to create a lesion within thetissue. In some such medical applications, it may be necessary to use aradiofrequency medical device to treat a region of tissue that has anelectrically conductive object positioned therein. For example, in somepatients there may already be a stent present within the vasculaturewhich has previously been placed to treat a medical condition, but whichmay have now become occluded or stenosed over time. Radiofrequencytreatment may now be an option in order to create a passageway throughthe occlusion or stenosis within the stent lumen. However, the use ofradiofrequency through or adjacent a conductive object such as ametallic stent creates a unique challenge. While it is desirable to useradiofrequency to traverse through a region of tissue such as anocclusion or stenosis, it is undesirable to apply radiofrequency whilethe medical device is too close to or in contact with the electricallyconductive object as it may make the electrically conductive object anenergy delivery conduit resulting in injury to the patient throughexcessive heating and/or charring of tissue around the electricallyconductive object.

Conventional devices lack the ability to deliver energy near aconductive object while ensuring delivery is stopped or controlled ifthe device is too near or in contact with the electrically conductiveobject. Furthermore, convention devices lack the ability to provide theuser with information about the proximity of the medical device to theelectrically conductive object. As such there is a need in the art toprovide an energy delivery system and method to allow a user to useradiofrequency energy to treat a region of tissue within the patient'sbody in the vicinity of an electrically conductive object whileproviding an indication of the proximity of the medical device to theelectrically conductive object to allow the user to re-direct themedical device away from the conductive object.

Alternatively, in some medical procedures, it may be desirable to directa medical device towards an electrically conductive object that may bepositioned, for example, within a region of tissue within the patient'sbody to function as a target to direct the medical device to a desiredtarget tissue location. The present inventors have recognized a need inthe art for an energy delivery system that assists in navigation of amedical device towards a target site by providing proximity informationbetween the medical device and the electrically conducive object.

The present inventors have thus discovered a method of delivering energyto a region of tissue within a patient's body using a medical devicethat is coupled to an energy delivery system. In accordance with anembodiment of the present invention, the method allows for use of amedical device near an electrically conductive object by providingproximity information that indicates the proximity of the medical deviceto the electrically conductive object. As such, in some embodiments themethod and system of the present invention enable a user to direct amedical device away from an electrically conductive object whileallowing the user to operate in the vicinity of the object by providingrelative proximity information to the user that is relevant to themedical device and electrically conductive object. Some such embodimentsprovide for earlier detection as the device is approaching an objectwhich may provide greater opportunity for course correction and mayassist with successful completion of a medical procedure. In otherembodiments, the method and system of the present invention allow theuser to direct the medical device towards an electrically conductivetarget object and to guide the medical device towards a desired targetlocation by providing an indication of the proximity of the medicaldevice to the electrically conductive object. Particulars of suchembodiments are described in Further detail herein below with respect toFIGS. 6 a-6 c.

Some embodiments of the present invention thus provide a method ofdelivering energy in a patient's body near an electrically conductiveobject in a safe and effective manner. In accordance with this approach,the present inventors have reduced to practice an embodiment of a methodthat detects if an energy delivery parameter of a medical device crossesa threshold and provides a relative measure of proximity between themedical device and the conductive object. In some embodiments,alternatively a method is provided that assesses the extent of thedeviance or variance between the one or more measured values of theenergy delivery parameter and the threshold to provide a relativemeasure of proximity between medical device and the conductive object.

Such embodiments are particularly useful and advantageous when aprevious medical procedure has involved placement of a conductive objectwithin the body and the treatment of the patient necessitates deliveryof energy near or adjacent the conductive object while preventingcontact with the conductive object. An example may be a region ofvasculature that has an occlusion or stenosis at the site of a previousstent placement. Such embodiments are also particularly useful inprocedures that require a medical device to be guided towards a desiredtarget site where the target site may have a conductive objectpreviously placed therein such as a guidewire or a snare. An embodimentof a method of the present invention is provided that assesses theproximity of medical device to the conductive object and providesinformation on the relative proximity between the two to guide themedical device towards the conductive object. This may help reduceprocedural time and complexity for certain medical procedures such asfor example a Transjugular Intrahepatic Portosystemic shunt (TIPS)procedure for example, as described in U.S. provisional application No.62/208,404, filed on Aug. 21, 2015 and U.S. provisional application No.62/208,138, filed on Aug. 21, 2015. These application are herebyincorporated by reference in their entirety. Detailed embodiments ofsuch examples of the present invention are described in herein belowwith respect to FIGS. 6A-6C.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of certain embodiments of the present inventiononly. Before explaining at least one embodiment of the invention indetail, it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is capable of other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein is for the purposeof description and should not be regarded as limiting.

In accordance with an embodiment of the present invention, a method isdisclosed for delivering energy within a region of tissue within apatient's body. The method helps avoid significant arcing while allowinguse of an energy delivery device in the vicinity of an electricallyconductive object such as a metallic object. An energy deliveryparameter is monitored during the delivery of energy. The value of theenergy delivery parameter is compared to a predetermined magnitudethreshold to determine if the value exceeds or falls below thepredetermined threshold to ascertain if there is significant arcing. Theenergy delivery is then controlled based on the extent of the arcingobserved.

It should be understood that, throughout this specification, the terms“cross” or “exceed”, in various forms, are used interchangeably to referto the value of a parameter extending beyond the threshold, includingboth above the threshold (for example, in the case of an “upperthreshold”) as well as below the threshold (for example, in the case ofa “lower threshold”). The terms “cross” or “exceed” may be used ineither scenario and are not intended to be limited to either above orbelow the threshold.

A medical treatment system, in accordance with embodiments of thepresent invention as shown in FIGS. 1 a and 1 b, comprises an energydelivery device or medical device 10 coupled to an energy source 200 toprovide energy to a region of tissue within a patient's body. In onespecific example, a radiofrequency (RF) energy delivery device is usedin an electrosurgical application to cut or channel through a region oftissue. Energy is provided to generate an arc to enable cutting at theregion of tissue. In some embodiments, as shown in FIGS. 1 a and 1 b, anenergy delivery device 10 is used in a region of a patient's body 90where an electrically conductive object 50, such as a metal object, isdeployed or positioned. In such embodiments, the present inventionallows for delivery of energy adjacent or near the electricallyconductive object 50.

In one example, the electrically conductive object 50 is a stent 52 andan energy delivery portion 12 of an energy delivery device 10 may bepositioned adjacent or close to the stent 52. Energy is provided by theenergy delivery source or energy source 200 and through the energydelivery device 10 into the region of tissue. A change in an energydelivery parameter associated with the delivery of energy by the medicaltreatment system, may be observed due to the proximity of the stent 52to the energy delivery portion 12. For example, a change in voltage, alower impedance, an increased power output or an over-current or acurrent spike may be observed when there is arcing. The delivery ofenergy from the energy delivery device 10 may be prevented, for exampleby the system, if the arcing is significant and the extent of the arcingexceeds a sensitivity threshold. This may help avoid lesion formation bypreventing RF energy from being transmitted through a low impedancemetal object, such as stent 52. Thus, the delivery of energy from theenergy delivery portion 12 of device 10 may be prevented when the energydelivery portion 12 of device 10 is positioned adjacent to or in contactwith an electrically conductive object 50, for example, a metal objectsuch as a stent.

In one embodiment of the present invention, a fault detection circuit400, as shown in FIGS. 1 a and 1 b, may be used to monitor an energydelivery parameter such as current. If the energy delivery parametercrosses a predetermined threshold, the fault detection circuit 400detects or records an error. In the embodiments described herein, anerror may mean an error and/or a fault. In a specific example, if themonitored current is 2 Amps and it exceeds a current magnitude thresholdof 1 Amp, an error in the form of an over-current is detected. Theextent of the faults may be determined and the controller 450 maycontrol the output of the energy delivery device based on the extent ofthe faults detected and/or recorded. If the extent of the errors exceedsa sensitivity threshold before the expiry of a predetermined timeperiod, an event or alert may be triggered and energy delivery may becontrolled. For the purposes of the present specification, “expiry of apredetermined time period” can mean, for example, (i) over a specificduration of time OR (ii) by a predetermined point in time relative to,for example, the beginning of the treatment procedure or the initiationof energy delivery. In one example, the ‘extent’ of the errors ismeasured over the course of a predetermined duration or time period.

As noted above, once the extent of the errors exceeds a sensitivitythreshold, an event or alert may be triggered. In some embodiments, anenergy delivery and control system may provide an indication to the userand may provide the user the option of disabling the energy. Forexample, the energy delivery and control system may provide an errorwarning or other alert to the user, for example on a screen associatedwith the energy source. Alternatively, the delivery of energy may beautomatically affected based on the extent of errors detected. Forexample, energy delivery may be stopped or disabled, the delivery ofenergy may be reduced, and/or one or more of the energy deliveryparameters may be altered.

In one embodiment, the extent of the errors may be ascertained bydetermining the resultant magnitude of the errors detected and/orrecorded. In one embodiment, if the magnitude of the detected and/orrecorded errors exceeds a predetermined sensitivity threshold, energydelivery may be controlled as described herein above.

In a specific example, as outlined above, if the monitored or measuredcurrent is 2 Amps whereby it exceeds a current magnitude threshold of 1Amp, an error in the form of an over-current is detected. In furtherdetail, the sensitivity threshold to measure the extent of the error(s)may be predetermined to be an amount of charge proportional to a 4 Ampcurrent. For example, if five 2 Amp over-currents are detected, then theresultant total magnitude of these over-currents (i.e. the amount of theover-currents that is above the ‘current magnitude threshold’ of 1 Amp,added together), is determined. If this resultant magnitude ofover-currents, which in this example would be equal to about 5 Amps(i.e. five over-currents where each exceeded the threshold by 1 Amp),exceeds the sensitivity threshold (4 Amps), an event may be triggeredand energy delivery may be controlled.

In another example, if one 6 Amp over-current is detected (exceeding thethreshold by 5 Amps), then the resultant magnitude of this singleover-current (i.e. the amount of the current that is above the ‘currentmagnitude threshold’ of 1 Amp) is determined. If this resultantmagnitude (which in this example is equal to 5 Amps) exceeds thesensitivity threshold (4 Amps), energy delivery may be controlled.

In one example, the energy delivery device comprises an RF wire. Asshown in FIG. 1 a, current in the RF return pathway or the ground (GND)return pathway 16 from a grounding pad 22 (monopolar operation) may becoupled to the fault detection circuit 400. In another example, ground(GND) return current from the energy delivery device (bipolar operation)may be coupled to the fault detection circuit 400. Alternatively, asshown in FIG. 1 b, the RF output current at the output of the energysource (i.e. along the RF energy delivery pathway 18) is coupled to thefault detection circuit 400. In some embodiments, the fault detectioncircuit 400 may be a component of the energy source 200. In alternateembodiments, the fault detection circuit 400 may be coupled to theenergy source 200 through a controller 450. In other embodiments, thefault detection circuit may be a separate entity and may be operable tobe used with any RF generator. A relay may be used to turn off ordisable RF energy delivery in response to the detected fault(s).

The energy delivery parameter may be monitored continuously orintermittently. Also, the energy delivery parameter may be monitoredeither during the delivery of energy (i.e. concurrently with the step ofdelivering energy) or shortly after the step of delivering energy (i.e.energy delivery and monitoring may be performed in an alternatingmanner). In other words, the steps of delivering energy and monitoringmay be performed either contiguously or substantially simultaneously.Furthermore, in some embodiments, the energy may be deliveredcontinuously, intermittently or in a pulsed manner.

The monitored energy delivery parameter may be any one of, or acombination of, current, voltage, impedance or power. Alternatively,other suitable energy delivery parameters may be used and monitored. Forexample, if a decrease in output impedance or voltage, or an increase inoutput power or current, is detected by a fault detection circuit, oneor more errors may be detected and/or recorded. Thus, if a value of theenergy delivery parameter is not within a predetermined range or crossesor exceeds or does not meet a specified magnitude threshold, one or moreerrors may be detected and/or recorded. In other words, if the value ofthe energy delivery parameter falls below a predetermined magnitudethreshold or exceeds a specified magnitude threshold (i.e. if the energydelivery parameter crosses a magnitude threshold) an error is detected.

Additionally, an extent, for example the quantity or quality, of anysuch detected errors may be determined or assessed. The delivery ofenergy may be controlled in response to the extent of errors detected.For example, the delivery of energy may be controlled if the quantity orquality of the detected exceeds a sensitivity threshold before theexpiry of a predetermined time period. In some embodiments, thesensitivity threshold may be defined by a threshold number of errors, athreshold value of the energy delivery parameter or a time threshold. Inalternate embodiments, the sensitivity threshold may be defined in termsof a threshold limit of an amount of charge that can be accumulatedbefore energy delivery is controlled. In some embodiments, thesensitivity threshold may be a voltage threshold. In one particularembodiment, the sensitivity threshold may be a voltage thresholdassociated with the amount of charge that can be stored by a capacitor.

In some embodiments, the step of determining the extent of errorsdetected may comprise a step of determining the number of errorsdetected. In such embodiments, energy delivery may be controlled if thenumber of faults or errors exceeds a threshold quantity (i.e. if theamount of errors detected, regardless of the absolute value of eacherror, exceeds a predetermined threshold) before the expiry of apredetermined time period.

In other embodiments, the step of determining the extent of errorsdetected may comprise a step of determining the resultant magnitude ofthe one or more detected values of the energy delivery parameter. Thedelivery of energy from the energy delivery device may be controlled inresponse to the resultant magnitude of the one or more values of theenergy delivery parameter. More specifically, energy delivery may becontrolled if the resultant magnitude (or in other words sum) of the oneor more values of the energy delivery parameter exceeds a thresholdvalue before the expiry of a predetermined period of time. For example,the energy delivery parameter may be current, and charge from anyover-currents may be stored in a capacitor. If sufficient charge isaccumulated before the capacitor discharges completely, an event may betriggered and energy delivery may be controlled. In one example, thesensitivity threshold may correspond to a current value of 4 Amps whichmay correspond to the amount of charge that can be stored by thecapacitor. If two 3 Amp over-currents (that each exceed a magnitudethreshold of 1 Amp) are detected, then the capacitor may become fullycharged (depending on the rate of discharge of the capacitor, fullycharging the capacitor may require slightly more over-current to bedetected) and the energy delivery may be controlled in response.

In still another embodiment, the step of determining the extent oferrors detected may comprise a step of determining the duration of timeduring which the one or more errors are detected. In other words theextent of the error is determined by measuring the length of time, orduration, over which the error existed. The delivery of energy from theenergy delivery device may be controlled in response to the duration oftime during which the one or more faults are detected. Energy deliverymay be controlled if the duration of time for the one or more faultsdetected exceeds a time threshold before the expiry of a predeterminedperiod of time. In some embodiments the time threshold may be less thanthe predetermined period of time. In other embodiments, the timethreshold may be equal to the predetermined period of time.

In some embodiments, the monitored energy delivery parameter may becurrent and the extent of the over-currents detected within a timeperiod may be determined. The controller 450 may adjust the delivery ofenergy through the energy delivery source 200 based on the extent of theover-currents detected/recorded. As described above, in one example, thepower may be shut off or the energy delivery otherwise disabled if thenumber of over-currents detected exceeds the sensitivity thresholdbefore the expiry of a time period. If a large number of over-currentsare detected, an event may be triggered and energy delivery may bedisabled. As an illustration of this embodiment, the sensitivitythreshold for the quantity of over-currents detected may be preset toabout 10. If the number of over-currents detected exceeds 10 within, forexample, a time period of about 300 us, an event is triggered and energydelivery may be controlled.

In some embodiments, the monitored energy delivery parameter may beimpedance. One or more errors may be detected, if, for example, theimpedance seen by the device falls below a threshold impedance limit. Inone example, the initial value of the measured impedance may be in therange of about 200Ω. As energy is delivered via the energy deliverydevice, the measured impedance may rise to be in the range of about1500Ω. Once arcing is initiated the measured impedance may drop to belowabout 100Ω. In one example, as the impedance drops below the thresholdimpedance, which may be, for example, 100Ω, one or more errors may bedetected. After an arc is observed, the measured impedance may riseagain to about 1500Ω. Once another arc is observed, the measuredimpedance may drop once again to below about 100Ω. In one example, theextent of the errors may be determined by determining the number oftimes the measured impedance drops below about 100Ω. Energy delivery maybe controlled if the extent of errors detected is greater than thesensitivity threshold. In the aforementioned example, the sensitivitythreshold may be defined as a predetermined number of errors. Energydelivery may be controlled if the number of times the impedance dropsbelow the threshold impedance (e.g. 100Ω), before the expiry of a timeperiod, is greater than the predetermined sensitivity threshold number.Thus, the delivery of energy from the energy delivery device may becontrolled in response to the number of errors detected before theexpiry of a predetermined time period.

In another example, the measured impedance may remain at or below about100Ω for some time. In such an example, the extent of the errors may bedetermined by determining the duration of time over which the impedancedrops below the threshold impedance. The energy delivery may becontrolled if the extent of errors detected exceeds a sensitivitythreshold which, in this example, may be defined as a time threshold.Thus, energy delivery may be controlled, if the duration of time duringwhich impedance is below the threshold impedance exceeds the timethreshold (before the expiry of a predetermined time period). In someembodiments, the time threshold may be equal to the predetermined timeperiod. In other embodiments, the time threshold may be less than thepredetermined time period.

In one example, the monitored energy delivery parameter may be currentfrom the Ground Return (GND) of the energy delivery device or the outputcurrent from the energy source in the energy delivery pathway. Thecurrent may be monitored using a fault detection circuit 400 as shown inFIGS. 1 a, 1 b and FIGS. 2 and 3. Whenever a current spike is detected,it may constitute an error and the error can be detected and/orrecorded. In other words, when the measured current crosses or exceeds apredetermined current threshold (for example, either during the positiveor negative cycles of an RF waveform), an error in terms of anover-current is detected. The extent of the errors or faults in terms ofover-currents may then be determined or assessed. If the extent of theseover-currents exceeds a sensitivity threshold before the expiry of apredetermined time period, energy delivery may be controlled by thecontroller 450. In one embodiment, the extent of the over-currents maybe ascertained by determining the resultant magnitude of theover-currents detected. In one embodiment, if the magnitude of thedetected and/or recorded over-currents exceeds a predeterminedsensitivity threshold, energy delivery may be controlled. In oneexample, a capacitor, such as capacitor 516 a shown in FIG. 4 a, may beused to determine the resultant magnitude of the detected over-currents.In other words, the amount of charge from the over-currents (thatexceeds the magnitude threshold) is accumulated and stored within thecapacitor. The charge may be periodically discharged by the capacitor.Thus, as charge accumulates on the capacitor some of it is dischargedintermittently by the capacitor in between over-currents. Once enoughcharge has accumulated on the capacitor an event may be triggered andenergy delivery may be controlled as described hereinabove.

In one example, the extent of the over-currents detected may involvedetermining the number of over-currents detected. The sensitivitythreshold may be determined by a set number or quantity of over-currentsthat have to be detected and/or recorded before energy delivery iscontrolled. If the number of over-currents detected exceeds apredetermined quantity, an event can be triggered which disables energydelivery. Thus, the sensitivity threshold may be defined or adjustedsuch that energy delivery is not disabled until after a predeterminednumber of over-currents or arcs have been detected and/or recorded. Thisallows the physician to continue to cut and steer away after anover-current or arc is detected. The output energy stays at the nominalvalue required for RF cutting and as the energy delivery device ormedical device 10 is moved away from the metal object it can continue tocut. Thus, the orientation or position of the energy delivery portion 12may be re-adjusted by moving it around or away from the electricallyconductive object 50 such as a metal object, even if a few over-currentsare detected while power is being delivered. This allows a user to cutclose to the metal object. This further allows steerabilitiy of thedevice around the low impedance metal object and allows a pathway to becreated by cutting around or close to the metal object. In one specificexample, the user may continue to cut and create a pathway in a vessellumen, such as through an occlusion or a stenosis at the location wherea stent has been deployed. The energy delivery device or medical device10 may continue to deliver energy and cut while traversing through astent lumen positioned within a body lumen, such as a blood vessel.Thus, depending on the setting of the sensitivity threshold, even afterseveral over-currents, the user can steer device 10 away from the stentwhile continuing to deliver energy.

In accordance with one broad embodiment of the present invention, amethod is disclosed for delivering energy to a region of tissue within apatient's body. FIG. 4 b is a flow chart illustrating an example of sucha method. As shown by step 304, an energy delivery device may bepositioned within a region of tissue at a target location within apatient's body. At step 306, an RF power source may be used to supply RFenergy to the energy delivery device. The energy delivery parameter thatis monitored may be the current output from the ground return pathway ofthe energy delivery device. The measured values of the current arecompared to a predetermined current range or magnitude threshold. In oneexample, the range of currents or current threshold may reflect normaloperational currents required for cutting. In another example, thecurrent magnitude threshold may reflect normal operational currentsgenerated during RF ablation. The current magnitude threshold may be anadjustable threshold. In one specific example, the energy deliverydevice is an RF cutting device and the normal operational thresholdcurrents are in the range of less than about 3 Amperes (Amps). Inanother example, the threshold current may be less than about 2 Amps. Inanother example, the threshold current may be less than about 1 Amp. Instill another example, the threshold current may be in the range ofbetween about 2 Amps to about 3 Amps. In another embodiment, the energydelivery device may be a radiofrequency ablation device and the normaloperational current threshold may be less than about 1 Amp. In anotherexample, the threshold current may be about 1.5 Amps.

At step 308, the measured current is analyzed to determine if it isgreater than the predetermined threshold or range. If the current haspeak values that exceed the current magnitude threshold or normaloperational currents, at step 310 an excess current or over-current isrecorded. If the monitored current is within the range of normaloperational currents (below the predetermined current threshold), thenthe delivery of energy through the energy delivery device will not beinterrupted and energy delivery can continue at step 306 and the currentcan continue to be monitored. At step 312, a determination is made toassess whether or not the extent of over-currents recorded within a timeperiod is greater than the sensitivity threshold and, if it is, then theenergy delivery may be adjusted at step 314. In one example, energydelivery may be stopped. In some embodiments, the extent ofover-currents recorded may be determined in terms of the sum ormagnitude of the over-currents recorded. In other embodiments, theextent of over-currents recorded may be determined in terms of thenumber or quantity of over-currents recorded. If the extent ofover-currents is still below the sensitivity threshold, then at step 306the energy delivery is continued while monitoring the current.

Referring back to FIGS. 2 and 3, a fault detection circuit 400 may beused to determine if the energy delivery portion 102 of device 100 isnear or adjacent to an energy conductor such as a stent 52 or a snareduring RF delivery. The fault detection circuit 400 may be used todetect, for example, currents in the ground (GND) return path of theenergy delivery device 100 or currents at the RF output 18 of the energysource in the energy delivery path. If peak currents or over-currentsare detected that exceed typical predetermined operational currents, anevent may be triggered and energy delivery through device 100 may bestopped or otherwise affected. The fault detection circuit 400 may beintegral with the RF energy delivery source 200, which may be an RFgenerator. In other embodiments, fault detection circuit 400 may be aseparate component of the medical treatment system. In one example, thefault detection circuit 400 may receive input current from the groundreturn pathway 16 from a grounding pad positioned on the patient's bodyin a monopolar application. Alternatively, the fault detection circuit400 may receive input current from a ground return pathway from theenergy delivery device 100 in a bipolar application (not shown).

The input current may be sensed using a current to voltage converter 404as shown in FIGS. 2 and 3, which converts the measured current (eitherat RF output or GND return) of the device into voltage. In someembodiments, a voltage sense transformer may be used. In otherembodiments, any current to voltage converter, for example a currentsense transformer, may be used. In still other embodiments any means tosense the current may be used. In one specific example, a current sensetransformer 504 is used as shown in FIG. 4 a, and the output of thecurrent sense transformer 504 may be connected to a high-pass filter506. The high-pass filter allows for adequate rejection of thefundamental or operating frequency of the RF system. This may aid indetection of over-currents. The high-pass cut off can change based onthe operational frequency. In one specific example, as shown in FIG. 4a, the high pass filter is an RC filter 506. The RC filter can be asingle pole filter or a multi-pole filter. The output of filter 506 maythen be routed to an input comparator 408 a, which, in this example, isa positive comparator that can detect positive current peaks. Anadditional input comparator may be used such as a negative comparator408 b that has the ability to detect negative current peaks. In oneexample, comparators 508 a, 508 b may be used as shown in FIG. 4 a.

The circuit may have an adjustable voltage threshold 410 which may beachieved through the use of a potentiometer 510 as shown in FIG. 4 a. Inother words the input comparators 408 a, 408 b may have an adjustablevoltage threshold. This allows the current threshold for detectingover-currents to be adjusted as desired. In alternate embodiments thevoltage threshold may be fixed. The output of the input comparators 408a, 408 b may be fed into the Discriminator circuit 430. In one example,as shown in FIG. 2, the Discriminator Circuit 430 has an analogimplementation which allows the magnitude of the over-current(s) to berecorded. In other words, the extent of the over-currents detected isdetermined in terms of the sum of the magnitude of the over-currentsdetected. I.e. the actual values of the currents that are above themagnitude threshold have been recorded and are added together.

As the high-frequency current peaks (over-currents) are detected by thetwo input comparators 408 a, 408 b, the over-currents are fed into, forexample an OR gate 412 to create a pulse train. In the embodiment shownin FIG. 2, as noted above, the Discriminator Circuit 430 has an analogimplementation. The Discriminator circuit 430 has a low pass filter 416which presents a slowly-changing average of this pulse train to theoutput comparator 418 of the Discriminator circuit 430. If the pulsesare frequent enough, the voltage at the input of comparator 418 willrise above the sensitivity threshold and will trip the DiscriminatorCircuit output.

The low pass filter 416 may help reduce the risk of false positives interms of false over-currents being detected. In one example, the lowpass filter 416 may be an RC filter 516 at the input of the comparator.The RC filter 516 allows the charge from the detected over-currents tobe stored within capacitor 516 a. The charge from an over-current orcumulative charge from multiple over currents is stored by the capacitor516 a within the RC time constant of the capacitor. In one example, theRC time constant of the capacitor is about 100 μs. The voltage at thecapacitor 516 a node is fed as an input of the output comparator 518.When the voltage at the capacitor 516 a node is equal to or greater thanthe sensitivity threshold voltage input to the output comparator 518,this determines that the extent (i.e. in this embodiment, the sum, or inother words, the resultant magnitude) of the detected over-currentsexceeds the sensitivity threshold.

In one example, the sensitivity threshold may be fixed. In anotherexample, the output comparator 418 may have an adjustable sensitivitythreshold 420 a. In one example a potentiometer 520 may be used toadjust the sensitivity threshold by changing the voltage at the input ofthe output comparator 418. This changes the voltage to which thecapacitor 516 a must charge and proportionately the length of timerequired for the charge to accumulate on the capacitor 516 a. If thepotentiometer is set to a higher voltage, than a greater number ofover-currents may occur before the controller allows the power supply tothe energy delivery device to be shut off, thereby disabling energydelivery. In one example, the sensitivity threshold may be set to allow10×1 Amp current peaks or over-currents to be detected within a 100 μstime period prior to disabling the energy delivery. Alternatively, or inaddition, the sensitivity threshold may allow 5×2 Amp current peaks orover-currents to be detected. In another embodiment, the sensitivitythreshold may be set to allow, for example, 10×3 Amp current peaks to bedetected within a 100 μs time frame. Other examples are possible aswell.

The output of the comparator may then be conveyed to a controller, whichcontrols the delivery of energy through the energy delivery device. Inone embodiment, the controller may prevent the delivery of energythrough the energy delivery device based on the sum or magnitude ofover-currents detected. In other words the controller may shut-off thepower delivery based on the extent of over-currents detected.

With reference now to FIG. 3, an alternate embodiment is shown in whichthe Discriminator Circuit 430 comprises a discrete or digitalimplementation. The number of current peaks may be detected and, ratherthan a low-pass filter and comparator, a digital counter 422 may beused. The digital counter 422 may have an external reset. In oneexample, if the number of over-currents detected before the counter isreset exceeds a digital threshold, the energy delivery may be disabled.The sensitivity threshold in the digital implementation of theDiscriminator circuit 430 is the digital threshold, which represents thenumber of pulses or over-currents that should be detected before theoutput of the Discriminator Circuitry 430 is asserted and conveyed tothe controller. The controller may then control the delivery of energythrough the energy delivery source based on the number of over-currentsdetected. In one example, the digital sensitivity threshold 418 b may bevariable, or may be adjustable by the user. In this example, the numberof over-currents that must be detected by the counter 422 before anoutput is asserted, can be changed as desired by the user. In anotherembodiment, the sensitivity threshold may be fixed and the number ofover-currents that must be detected by the counter 422 may thus be fixedas well.

With reference now to FIGS. 5 a and 5 b, block diagrams of a medicaltreatment system in accordance with embodiments of the present inventionare shown. An energy delivery source is shown which includes a faultdetection circuit. In some embodiments the fault detection circuit maybe a separate component of the medical treatment system. In one example,the fault detection circuit receives input from the ground return asindicated by “RF−”, in FIG. 5 a. In another example, the fault detectioncircuit receives input from the RF Amplifier of the energy deliverysource, as shown in FIG. 5 b.

The RF Amplifier of the energy delivery source of the generator providesinput current to the energy delivery device shown as “RF+”. The RFamplifier is coupled to an FPGA (field programmable gate array) whichmay be coupled to an RF board Controller (RFC) and a User InterfaceController (UIC) which help control the output to the energy deliverydevice. The Control circuitry, which includes the RFC, the UIC and theFPGA, receives feedback from the fault detection circuit and can controlthe delivery of energy from the energy delivery source based on theinput received from the fault detection circuit. Once the DiscriminatorCircuit (not shown) of the fault detection circuit determines that theextent of the over-currents (magnitude or sum of over-currents) exceedsa sensitivity threshold, the output generated by the Fault DetectionCircuit may be conveyed to a latch and its output may be set to high.This output may then be conveyed to the Control Circuit, which allowsthe energy delivery from the energy delivery source to be controlledbased on the output of the Fault Detection Circuit. Thus the delivery ofRF signal from the RF amplifier may be stopped. The latch output maythen be reset. In some examples, the latched signal is detected viaserial read or interrupt. (The Peak Detector and High Pass Filter of theFault Detection Circuit do not impede flow of RF current, but rathermonitor it). The medical treatment system may also include a featureallowing a user to disable the arc-to-metal-detection function.

With further reference to FIGS. 5 a and 5 b, the current from the outputof the energy delivery device is received as input into the current tovoltage converter and high pass filter. In a specific example, the highpass filter is a 1.5 MHz nominal −3 db point single-pole high passfilter. Furthermore, in one specific example, the Peak Detectoractivates for current spikes of either polarity that exceed 40 ns induration at a threshold current value of 1.7 A. In other words the PeakDetector detects an error/fault if the current exceeds 1.7 A for aduration of at least about 40 ns. The energy delivery is then controlledif the extent of errors or faults detected exceeds a sensitivitythreshold. The sensitivity threshold may be defined or set based on oneor more of the magnitude (in terms of the amplitude) as well as thepulse width of the pulse train of current to be detected. In oneembodiment, the sensitivity threshold is set as a time threshold orduration of about 300 μs±30 μs. In an example of this, if pulses (thatare at or above a threshold amplitude of 1.7 Amps having a pulse widthof about 113 ns) are observed for a duration of at least about 300 μs±30μs, energy delivery may be controlled. More specifically, once the Peakdetector has been supplied with a continuous string of pulses forduration equal to or exceeding the sensitivity threshold of about 300μs±30 μs, the Metal Detector within the Fault detection circuitry isactivated.

In another example, the sensitivity threshold is set as a time thresholdor duration of about 30 μs±3 μs. If pulses (that are at or above thethreshold amplitude of 1.7 Amps having a pulse width of about 500 ns)are observed for a period of time greater than or equal to about 30 μs±3μs, the energy delivery may be controlled. Thus, once the Peak detectorhas been supplied with a continuous string of pulses (having a pulsewidth of at least about 500 ns) for duration equal to or exceeding asensitivity threshold of about 300 μs±3 μs, the Metal Detector isactivated. The output generated by the Fault Detection Circuit may thenbe conveyed to the Control circuitry to modify the output of the energydelivery device.

As mentioned above, the Control circuitry which includes the RFC, theUIC and the FPGA receives feedback from the fault detection circuit andcan control the delivery of energy from the energy delivery source basedon the input received from the fault detection circuit.

In alternate embodiments, the energy delivery device may be used near anelectrically conductive object 50 that is a bare metal snare. In stillanother example, the electrically conductive object 50 may be an RFwire. In further examples, the electrically conductive object 50 may beany metal object positioned within a patient's body such as a metalscrew. In one example, the electrically conductive object 50 may be ametal RF wire or a snare that may be used as a target for positioningthe energy delivery device. In some embodiments, the electricallyconductive object 50 may be another electrosurgical device. In onespecific example, the electrically conductive object or device 50 may bea stent-graft and the medical treatment system may be used to create afenestration through a stent-graft through the delivery of RF energy. Inother words, the RF energy delivery device may be used to induce graftperforation of a stent-graft as discussed in U.S. patent applicationSer. No. 11/905,448, filed on Oct. 1, 2007, previously incorporatedherein by reference in its entirety. In one example, the stent-graft maybe positioned in a renal artery. In another example, the stent-graft maybe positioned in a branch of the aorta. In one specific example, themedical treatment system may be used to create a fenestration through astent-graft positioned in the thoracic aorta.

In various alternatives, the energy delivery device 10 may have anelectrically conductive energy delivery portion 12 along at least alonga portion of the energy delivery device. The energy delivery portion 12is coupled to the energy source 200 such that the energy delivery source200 provides RF energy to the energy delivery portion 12. The energydelivery portion 12 may comprise one or more active electrodespositioned on a portion of the energy delivery device 10. In oneembodiment, the energy delivery device is an RF energy delivery devicethat comprises at least one active electrode. In other embodiments, morethan one active electrode may be positioned on the energy deliverydevice.

In some embodiments of the present invention as disclosed above, theenergy source may provide energy in the range of between about 100 KHzto about 1.5 MHz. In one example the energy source is provided in theform of an RF generator that is capable of delivering energy in thefrequency range of between about 400 KHz to about 550 KHz, morespecifically, between about 450 KHz to about 480 KHz. In one example,energy is delivered at a frequency of about 460 KHz. The energy deliverydevice may be used to provide energy for a range of applications withina patient's body. This may include use in cardiac applications, fortreatment within a patient's vasculature.

In some embodiments, power may be provided at greater than about 30Watts. In some embodiments, the power may be supplied at greater thanabout 50 Watts. The voltage supplied may be greater than 200 Vrms. Insome embodiments the energy delivery device may be an RF cutting device.In some such embodiments, the voltage is supplied in the range ofbetween about 200 Vrms to about 300 Vrms. In some embodiments, thevoltage may be supplied in the range of between about 200 Vrms and 400Vrms. In other embodiments, the supplied voltage is greater than orequal to about 400 Vrms.

In an alternate embodiment, the energy delivery device may be an RFablation device with an active ablation electrode. In some embodiments,the voltage supplied may be greater than about 50 Vrms. The power may besupplied in the range of between about 2 Watts and about 8 Watts. Insome such embodiments, the Voltage may be between about 100 Vrms toabout 200 Vrms.

In one particular embodiment, as described previously and as describedfurther with reference to FIG. 6 a, a method is disclosed for deliveringenergy within a region of tissue within a patient's body. The methodhelps avoid significant arcing while allowing use of an energy deliverydevice or in words a medical device 10 in the vicinity of anelectrically conductive object 50 such as a metallic object. In oneparticular example, the metallic object is a stent 52, as shown, thatmay have previously been placed within the vasculature to treat acondition within the body, for example such as an aneurismal vessel wallor at the site of a stenosis. Embodiments of the present method allowfor an energy delivery parameter to be monitored during the delivery ofenergy from the medical device 10. The value of the energy deliveryparameter is compared to a threshold value to determine if the valueexceeds or falls below the threshold to ascertain if the medical device10 is in proximity to the electrically conductive object 50.Additionally, the values obtained for the energy delivery parameter maybe used to determine the relative distance between the medical device 10and the electrically conductive object 50. The orientation of themedical device 10 may be adjusted and the energy delivery may then becontrolled based on the relative proximity or distance determinedbetween the medical device 10 and the electrically conductive object 50such as the metal stent 52.

In some embodiments of the present invention, the energy deliveryparameter may be current and the distance may calculated as a functionof the electrical current that is detected. As illustrated in FIG. 6 a,if a low value of current is detected then the medical device 10, andmore specifically the energy delivery portion 12 of the medical device10 such as device electrode 14, is determined to be relatively far fromthe electrically conductive object 50, as shown in FIG. 6 a. In one suchexample, a baseline current value may be obtained as the medical device10 is being advanced into the patient's body and a current may bemeasured as the medical device 10 (and specifically the device electrode14) is closer to the electrically conductive object 50. If a low valueof current is detected relative to baseline value then the medicaldevice 10 (and the device electrode 14) is determined to be relativelyfar from the metallic object. On the contrary, in some examples, if ahigher electrical current value is obtained then the device electrode 14is determined to be closer to the metallic object. Still alternatively,if the current value exceeds a predetermined metal contact thresholdthat is indicative of metal contact error, the device electrode 14 isdetermined to be in contact with the metallic object. In some suchembodiments, the values or characteristics of the energy deliveryparameter may be mapped to physical distances in a physiologicallyrelevant model. As such, some embodiments of the present inventionprovide a means to detect proximity by providing relative distanceinformation between the medical device 10 and the electricallyconductive object 50.

As such some embodiments of the present invention provide an indicationto the user as to the relative distance the medical device 10 is awayfrom the electrically conductive object 50 such as a metallic objectduring the course of the procedure. In accordance with an embodiment ofthe present invention, a method is provided that provides earlierdetection of the metallic object as the medical device 10 is approachingit. More specifically, the method provides information relating to therelative distance between the medical device 10 and the metallic objectas the device 10 is being advanced, which may allow the physician toalter or correct the course or trajectory of the medical device 10 inorder to avoid the metallic object and/or deliver energy at a distancefrom the metallic object. Furthermore, it may allow the user to continuedelivering energy while substantially avoiding contact with the metallicobject.

In accordance with some embodiments of the present invention, a methodis provided that provides for monitoring an energy delivery parameter ofthe device 10, where the energy delivery parameter that is impacted bythe relative distance between the device 10 and the metallic object.This allows changes in the value of the energy delivery parameter to beused to provide an indication of the relative proximity of the device 10to the metallic object. As the value of the energy delivery parameterchanges, it is translated into a corresponding distancemeasurement/information to provide the user with an indication of therelative distance between the device 10 and the metallic object.Information about the proximity of the device 10 to the metallic objectand the correction of the device trajectory prior to contact of thedevice with the metallic object, may allow for greater opportunity forcourse correction to avoid contact with the metallic object whilecontinuing with the delivery of energy. This may allow for enhancedprocedural efficiency and/or success. As such, some embodiments of thepresent invention may provide relative distance information between thedevice 10 and the metallic object and may provide an enhanced method todetect proximity that may involve the use of one or more energythresholds to assess an energy delivery parameter.

More specifically, some embodiments of the present invention provide ameans for providing an indication of the proximity between a device anda metallic object without requiring contact of the device with themetallic object allowing the physician to avoid contact with themetallic object through course correction. In one specific example, asshown in FIGS. 6 b and 6 c, a method is disclosed for delivering energywithin a region of tissue within a patient's body using a medicaltreatment system, where the method provides for assessing proximitybetween the medical device 10 and the electrically conductive object 50such as metallic object, for example a stent 52. The medical treatmentsystem comprises a medical device 10 coupled to an energy deliverysource. A general method of the present invention comprises the steps of(1) delivering energy from the medical device; (2) advancing the medicaldevice to a target site within the patient's body; (3) measuring anenergy delivery parameter while energy is being delivered; (4) detectingif (a value of) the energy delivery parameter crosses a threshold; (5)if the threshold is crossed thereby indicating proximity of the deviceto a conductive object, determining the relative distance betweenmedical device and the conductive object based on (the detected valuesof) the energy delivery parameter; (6) determining if the distancebetween the medical device and metal object is decreasing; and (7) upondetermining that the distance between the medical device and theconductive object is decreasing, adjusting a position of the medicaldevice and repeating steps (3)-(7) until the medical device ispositioned at a desired distance from the conductive object.

More specifically, in some embodiments as shown in FIGS. 6 b and 7 a-7d, the energy delivery parameter is current. In some examples, the RFcurrent may be characterized and mapped to distance between the medicaldevice 10 and electrically conductive object 50 (such as a stent 52), asshown at step 100 a and as further illustrated in FIG. 8. In one suchexample, there may be a substantially linear relationship betweencurrent and distance values. In other examples there may be a slightlyexponential relationship between current detected and the distance themedical device 10 is from the electrically conductive object 50. In somesuch examples, an initial current value may be obtained as the medicaldevice 10 is initially advanced into the patient's body, as shown atstep 100 b in FIG. 6 a, to function as an initial base value or baselinecurrent value. This may also be used to confirm that the medical device10 is not near a metallic object. This is further illustrated in FIG. 7a. The baseline value represents a relatively low electrical currentvalue, which is recorded when the medical device 10 is outside the fieldof effect 54 of the electrically conductive object 50. For example, whenthe device electrode or energy delivery portion 12 is outside the fieldof effect of the electrically conductive object 50 e.g. metallic object(several centimeters), there is no increase in current and this is thebaseline current value.

The method then comprises delivering energy as the medical device isadvanced into the patient's body as shown by steps 101 and 102,respectively in FIG. 6 b. The current values are then measured whileenergy is being delivered at step 103. These measurements may, in someembodiments, be repeated substantially continuously as the device isbeing advanced. The next step involves checking if the current isincreasing beyond a threshold value at step 104 and detecting if a valueof the current crosses the threshold. If at step 105 a, the threshold iscrossed, it indicates proximity of the device to an electricallyconductive object. This is further illustrated in FIG. 7 b, as themedical device 10 and such the device electrode 12 enters the field ofeffect 54 of the electrically conductive object, the value of themeasured current is above the baseline threshold value.

In some examples, as noted above, the threshold value is equal to thebase value or the baseline value which is measure or calculated at thebeginning of the procedure, upon advancing the medical device to thetarget site within the patient's body. In other examples the thresholdvalue may be equal to a pre-determined value of the energy deliveryparameter, for example current. In some examples the threshold value maybe equal to less than about 1.0 Amps. In some examples, the thresholdvalue ranges from about 0.3 Amps to about 1.0 Amps. In a specificexample, the threshold value is equal to about 0.3 Amps.

In accordance with an embodiment of the present invention, once themeasured value of current is detected to be greater than the baselinethreshold value, the method then involves determining the relativedistance between medical device 10 and the conductive object 50 based onthe detected values of current at step 105 b. In some examples, as shownin FIG. 6 b, at step 105 c feedback may be provided to the user aboutthe distance values that are obtained. In some embodiments a method ofthe invention provides feedback that indicates to the user the relativedistance between the medical device 10 and the conductive object. Atstep 106 it is then determined if the distance between the medicaldevice and metal object is decreasing as the device is being advanced.This determination is made by comparing the distance measurementsdetermined as the device is being advanced. As illustrated in FIG. 7 c,as the device 10 is advanced further, the device electrode 12 entersfurther within the field of effect 54 of the electrically conductiveobject 52. As the distance between the device electrode or energydelivery portion 12 and the electrically conductively object 50decreases, the values of the measured current increase. Based on thevalues of current obtained, if it is determined that the distancebetween the medical device and the conductive object is decreasing, themethod of the present invention provides for adjusting a position of themedical device and repeating steps 103 to 107 until the medical deviceis positioned at a desired distance from the electrically conductiveobject 50. In some such examples, the medical device may encounter areasof radial boundaries/circles or contour profiles as it enters the fieldof effect 54 of the electrically conductive object. The radialboundaries represent a particular value for an energy delivery parametersuch as current. The radial boundaries are equidistant from theelectrically conductive object 50 and are at the same value of an energydelivery parameter. For example, the radial boundaries represent areasthat are equipotential in the case the energy delivery parameter isvoltage. Alternatively, the radial boundaries may represent areas thatare equicurrent, or in other words they may represent areas where thedetected current has the same value.

In some embodiments, the method of the present invention mayadditionally be used to provide feedback/indicate to the user, if thedistance between the medical device and the conductive object isincreasing or decreasing. In some examples the indication may beprovided at any one of steps 105 a to 107, shown in FIG. 6 b. In aspecific example, indication/feedback is provided to the user if thedistance between the medical device and metal object is determined to bedecreasing. In some examples, the step of providing anindication/feedback to the user comprises providing a visual indication.Alternatively, the step of providing an indication/feedback to the usercomprises providing an electrical control signal. Still furthermore, thestep of providing an indication/feedback to the user comprises providingan acoustic indication. In some such examples, the acoustic indicationis taken from the group consisting of a volume based acoustic indicationand a frequency based acoustic indication. In some embodiments, if theelectrical current is greater than about 1.7 Amps, it indicates directmetal contact. In some examples, if the electrical current values rangefrom between about 1.0 Amps to about 2.0 Amps, they are indicative ofdirect metal contact. In other examples, if the electrical currentvalues are greater than about 2.0 Amps, they are indicative of directmetal contact. Still in other examples, if the electrical current isequal to about 1.7 Amps, it provides an indication of direct metalcontact.

In some embodiments, at step 107, the step of adjusting a position ofthe medical device 10 comprises directing the device away from themetallic object as shown in FIG. 7 d. As the device moves away from thefield of effect 54 of the electrically conductive object the currentdecreases which is indicative of the distance increasing between thedevice electrode or energy delivery portion 12 and the electricallyconductive object 50. This in some embodiments it may be desirable toprovide proximity information to the user so the user can avoid contactwith the electrically conductive object 50 such as a metallic object.For example if a metallic object is a stent 52 which has been previouslyplaced within a vasculature within the patient's body to treat a medicalcondition. Then it is desirable to provide information to the physicianof the medical device 10 is approaching the stent 52 and to provide anindication to the physician if the medical device is too close to thestent 52. In one such example, the step of adjusting a position of themedical device (step 107) comprises moving the medical device 10 awayfrom the conductive object 50 until measurement no longer exceeds thethreshold. As such in some embodiments, a method of the presentinvention provides a negative feedback mechanism to prevent a medicaldevice 10 from contacting an electrically conductive object while stillallowing the medical device to deliver energy.

In an alternative embodiment, it may be desirable to provide thephysician feedback in procedures where it may be desirable to guide themedical device 10 towards the conductive object 50. In one such examplethe conductive object 50 may function as a guide or marker to facilitateadvancement of the medical device 10 towards a target site. In one suchexample, the electrically conductive object 50 comprises a secondarymedical device and the step of adjusting a position of the medicaldevice in accordance with the method of the present invention, comprisesmoving the medical device towards the secondary medical device. In suchexample, a method of the present invention facilitates advancement ofthe medical device 10 through the liver parenchyma from a hepatic veinto the portal vein in order to assist with a trans-jugular portosystemichepatic shunt (TIPS) procedure for example as described in more detailin U.S. provisional application No. 62/208,404, filed on Aug. 21, 2015and U.S. provisional application No. 62/208,138, filed on Aug. 21, 2015.These application are hereby incorporated by reference in theirentirety. In such embodiments, the secondary medical device may comprisea medical guidewire or a snare that is positioned within a portal vein.The method allows for adjusting the position of the medical device untilit is positioned adjacent the secondary medical device. Thus, in someembodiments of the present invention, the method of the presentinvention provides a positive feedback mechanism to allow a medicaldevice 10 to be directed towards the electrically conductive object 50which may be a secondary medical device. An additional example of amethod where it is desirable to direct a medical device towards asecondary medical device such as a snare or a guidewire is disclosed inU.S. application Ser. No. 13/912,244 filed on Jun. 7, 2013, which isalso hereby incorporated by reference in its entirety. This applicationdiscloses further details of a method of traversing an occlusion where amedical device is directed towards a secondary medical device that ispositioned on an opposite side of the occlusion and that functions as atarget to guide the medical device.

As such, some embodiments of the present invention enable the user tonavigate a medical device to either avoid or approach an electricallyconductive object 50 such as a metallic object. Some embodiments, asdescribed previously provide for a step of determining if the distancebetween the medical device and metal object is decreasing.Alternatively, some embodiments may provide for a step of determining ifthe distance between the medical device and metal object is increasing.If it is desired to avoid a target the user may then continue on thepath the device is travelling in. If it is desired that the medicaldevice is advanced towards the electrically conductive object which maybe functioning as a target, then the method comprises adjusting anorientation of the device to direct the device towards the electricallyconductive object.

In some examples described herein above, the step of adjusting aposition of the medical device 10 is performed automatically. In aspecific example, the step of adjusting a position of the medical device10 is performed automatically using an automated navigation system. Onesuch method comprises a step of additionally providing anindication/feedback to the user through an electrical control signalthat is receivable by the automated navigation system.

In another example the step of adjusting a position of the medicaldevice 10 is performed concurrently with a step of imaging the medicaldevice. For example, the step of imaging the medical device 10 may beperformed using an imaging modality taken from the group consisting of:fluoroscopy, magnetic resonance imaging, computerized tomography scan,electro-anatomical mapping and magnetic positioning system. It may alsobe helpful to image the medical device 10 concurrently with the steps ofadvancing the medical device 10 and measuring the base value of current.Still furthermore, any of the steps 100-107 of a method of the presentinvention may be performed concurrently with a step of imaging themedical device 10. In some examples, a method of imaging may be of thetype described in U.S. provisional application No. 62/208,138, filed onAug. 21, 2015 which is hereby incorporated by reference in its entirety.

In accordance with various embodiments of the present invention, theenergy delivery parameter may be selected from the group consisting of:current, voltage, phase, frequency and impedance.

As such some embodiments of the present invention as described hereinabove provide a method and means to provide metal proximity informationwithout requiring direct contact with a metallic object (e.g. a stent)before triggering an error or indication. While contact with a metallicobject may also provide useful information to the physician, providinginformation or knowledge that the medical device is approaching themetallic object may allow contact to be avoided altogether throughcourse correction. Furthermore, providing this additional feedback tothe operator may result in greater procedural success. By monitoring anenergy delivery parameter such current amplitude, voltage amplitude andphase of a radiofrequency (RF) signal, it is possible to determine therelative distance between the device and an electrically conductiveobject such as a metallic object. As such embodiments of the presentinvention provide a method that provides the ability to characterize andmonitor electrical energy delivery properties or parameters such ascurrent, voltage, phase and frequency and further provides mapping ofthese characteristics to physical distances in a physiologicallyrelevant model. Some examples of the present embodiment provide relativedistance information and have the ability to provide relative distanceinformation using one or more thresholds (which may in some cases befixed thresholds).

In some examples, a method of the present invention may be used ininterventional procedures near metal objects, where it is preferable toavoid contact with these objects altogether. In specific cases involvingstents that have previously been placed to treat chronic totalocclusions (CTOs), a medical device may be required to be advancedthrough the stent. In such cases where the device is inside a stent(which outlines the vessel wall), it may be desirable to stay as closeto the central lumen of the vessel as possible, in order to avoidunintentionally exiting the vessel wall (into the extravascular space).The method allows for monitoring gradual changes in electrical signalcharacteristics or values of the energy delivery that correspond withthe distance to the electrically conductive objects. In some examples asoutlined previously, the present invention monitors the amplitude(instantaneous value and change) in current of the RF signal, in orderto determine the relative distance between the device and theelectrically conductive object, such as a metallic object. The presentinvention can also be used to avoid contact with metallic objects duringminimally invasive interventional medical procedures. It canadditionally guide a physician on how the device orientation needs to bealtered in order to stay on-course to advance through a vessel lumen(for example in a case where the device electrode is inside a stent thatoutlines the vessel wall).

In some embodiments, an invention of the present invention provides theability to characterize and monitor the electrical signal properties(e.g. current, voltage, phase, frequency). It additionally allows formapping of distance between the device and the electrically conductiveobject such as a metallic object vs. a signal property (such as anelectrical signal property such as current amplitude). As outlinedpreviously, in one particular example, electrical current greater thanabout 1.7 Amps indicates direct metal contact. Whereas, when the deviceelectrode is outside field of effect of the metallic object (severalcentimeters), there is no increase in current-forming the baselinecurrent value. Then as the device electrode gets closer to the metallicobject, the electrical current will increase until the point of contact.The distance between the medical device and the metallic object can bedetermined by assessing the current values and as noted above, feedbackcan be provided to the physician regarding the distance between themedical device and the metallic object. This can be a visual indicatorsuch as scale bar, acoustic indicator (such as a volume feedback orsound frequency). The orientation of the medical device may be adjustedbased on the feedback. As described previously, some embodiments of theinvention require an electrosurgical device, RF energy source withcurrent measuring ability, presence of an electrically conductive objectsuch as a metallic object within the body which may be in the proximityof the electrosurgical device electrode during use and a feedbackmechanism to provide feedback/indication to the physician. A specificexample of such a method of the present invention has been describedpreviously as shown in FIG. 6 b.

In accordance with some alternatives of the present invention, analternative to measuring current amplitude, voltage, phase, frequency orimpedance may be monitored and measured. In some examples physiciannavigation may be used to reorient the device. Alternatively, automatednavigation system (e.g. a surgical robotic system) may be used toreorient and/or adjust the position of the device. In some examples, afluoroscopy based imaging or navigational modality may be used to assistwith the procedure. Alternatively, other imaging or navigationalmodalities may be used such as MRI, CT, electro-anatomical mapping,magnetic positioning system (GPS for OR). In some examples as notedpreviously, the electrically conductive object may be a metallic objectwithin the body. Alternatively, in addition to an electricallyconductive object, a method embodiment of the present invention may beusable with a highly conductive medium. The method may be used to avoidcertain tissues or cavities in the body (e.g. cerebrospinal fluid whichmay be quite electrically conductive). One example of an imaging methodmay be used as described in some examples, a method of imaging may be ofthe type described in U.S. provisional application No. 62/208,138, filedon Aug. 21, 2015 which is hereby incorporated by reference in itsentirety.

As still a further alternative of the present invention, a 3D imagingmodality may be used to image device and metallic object. (E.g. CT orpotentially MRI). These may be used in an interventional procedure.Alternatively, a method of the present invention may involve, placingmultiple neutral electrodes (grounding pads on the body and measuringthe current/impedance from the device to each of these locations. Thisdata may be used to provide triangulation methods to determine therelative position of the metallic object which may include a valuerepresenting distance as well as direction.

In one specific example, in accordance with a method of the presentinvention, a medical device may be advanced in a straight line towardsthe electrically object. A one dimensional view may be obtained of thedevice travelling in a straight line towards the electrically conductiveobject. Based on location of medical device relative to the tissue andelectrically conductive object a nominal value may be obtained. In oneparticular case, the medical device may be advanced through the centerof an electrically conductive object such as a stent, where the baselinemeasurement may represent a measurement taken along the linear pathalong the center of the stent. In some examples, the distance betweenthe metallic outer wall of the stent and the center location of themedical device may be mapped as a linear relationship in a tissue model.As the medical device deviates from the center trajectory towards theexterior wall of the stent the values of the current detected goes upfrom the nominal or baseline value where a current value of greater thanabout 1.7 Amps represents contact of the medical device with an exteriorwall of the stent, as shown in FIG. 9. The relationship between currentand distance may be a linear relationship as the medical device movesradially towards the exterior of the stent. An indication may beprovided to the user as the detected value of current goes up toindicate to the user that the medical device is moving radially towardsthe exterior of the stent. The indication additionally functions toindicate to the user to move the medical device back to the originalrelatively central position (within the stent). In some embodiments, thebaseline value is about 0.3 Amps and may represent the minimum baselinecurrent value. The value of the baseline current may be obtained with orwithout imaging and may function as an absolute reference value.

In some such embodiments, a step of imaging may be used in conjunctionwith measuring and monitoring current to ensure that the medical deviceremains at the nominal baseline value to ensure the device trajectory isthrough substantially a center of stent. In one example, the imagingmodality may be fluoroscopy and two images may be obtained to ensurethat the medical device remains substantially in a center of thecross-section defined by the stent. In one particular case, the twoimages are taken perpendicular to the plane of view (e.g. a bi-planarapproach). In one example, the two perpendicular view may be an A-P viewand a lateral view. Alternatively, the two views may be two versions ofoblique views, the Right Anterior Oblique (RAO) and the correspondingperpendicular view which is the Left Anterior Oblique (LAO). Once theviews are obtained, the method involves for checking for deviation ofthe medical device with respect to the center trajectory. Alternatively,CT or MRI cross-sectional views may be obtained-various slices may becaptured for an MRI view. Then using the initial view of the medicaldevice travelling through the center of the stent, if the device isfound to be getting close to the stent wall (for example from thecurrent values obtain), then cross-sectional views and/or imaging slicesobtained through subsequent imaging may be used to find out if themedical device is getting close to the stent edge or periphery. This maysupplement the information that is obtained through changes in currentsuch as increased values of current that may be observed. Then aposition of the medical device may be adjusted to move the medicaldevice trajectory such that is through the center of the stent. In somecases a stent of imaging such as fluoroscopy, MRI or CT may be used toassist with reposition or reorienting of the medical device.

In accordance with a broad aspect embodiments of the present inventioncomprise a method is disclosed for delivering energy within a region oftissue within a patient's body using a medical treatment system, themedical treatment system comprising a medical device coupled to anenergy delivery source, the method comprising the steps of: (1)delivering energy from the medical device; (2) advancing the medicaldevice to a target site within the patient's body; (3) measuring anenergy delivery parameter while energy is being delivered; (4) detectingif (a value of) the energy delivery parameter crosses a threshold; (5)if the threshold is crossed thereby indicating proximity of the deviceto a conductive object, determining the relative distance betweenmedical device and the conductive object based on (the detected valuesof) the energy delivery parameter; (6) determining if the distancebetween the medical device and metal object is decreasing; and (7) upondetermining that the distance between the medical device and theconductive object is decreasing, adjusting a position of the medicaldevice and repeating steps (3)-(7) until the medical device ispositioned at a desired distance from the conductive object.

In accordance with an additional broad aspect, embodiments of thepresent invention comprise a method for delivering energy within aregion of tissue within a patient's body using a medical treatmentsystem, the medical treatment system comprising a medical device coupledto an energy delivery source, the method comprising: (1) deliveringenergy from a medical device to material within a patient's body; (2)measuring an energy delivery parameter while the energy is beingdelivered; (3) detecting (an error if one or more values of) the energydelivery parameter crosses a threshold; (4) if the threshold is crossed,determining whether the medical device is sufficiently distanced from aconductive object to allow for safe delivery of energy to the patient'sbody, by assessing an extent (of the error/by which the one or morevalues of) the energy delivery parameter that cross the threshold; and(5) if the medical device is determined to not be sufficiently distancedfrom the conductive object, adjusting a position of the medical deviceand repeating steps (2)-(4) until the medical device is sufficientlydistanced from the conductive object.

In accordance with still an additional broad aspect, embodiments of thepresent invention comprise a method for delivering energy within aregion of tissue within a patient's body using a medical treatmentsystem, the medical treatment system comprising a medical device coupledto an energy delivery source, the method comprising the steps of: (1)delivering energy from the medical device to a material within apatient's body; (2) measuring return current while energy is beingdelivered; (3) detecting (one or more over-currents) if the returncurrent exceeds a threshold; (4) if the threshold is exceeded, assessingthe extent (of the one or more over-currents) by which the returncurrent exceeds the threshold to determine if the medical device issufficiently distanced from a conductive object; and (5) if the medicaldevice is determined to not be sufficiently distanced from theconductive object, adjusting a position of the medical device andrepeating steps (2)-(4) until the medical device is sufficientlydistanced from the conductive object.

Thus, as described herein, in accordance with various embodiments, amethod is disclosed for delivering energy within a region of tissuewithin a patient's body. The method helps avoid significant arcing whileallowing use of an energy delivery device in the vicinity of anelectrically conductive object such as a metallic object. An energydelivery parameter is monitored during the delivery of energy. The valueof the energy delivery parameter is compared to a predeterminedmagnitude threshold to determine if the value exceeds or falls below thepredetermined threshold to ascertain if there is significant arcing. Theenergy delivery is then controlled based on the extent of the arcingobserved.

The embodiments of the invention described above are intended to beexemplary only. The scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the broad scope of theappended claims. All publications, patents and patent applicationsmentioned in this specification are herein incorporated in theirentirety by reference into the specification, to the same extent as ifeach individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

We claim:
 1. A method is disclosed for delivering energy to a region oftissue within a patient's body using a medical treatment system, themedical treatment system comprising a medical device coupled to anenergy delivery source, the method comprising the steps of: (1)delivering energy from the medical device; (2) advancing the medicaldevice while delivering the energy; (3) measuring an energy deliveryparameter while advancing the medical device; (4) detecting whether ornot a value of the energy delivery parameter crosses a threshold; (5) ifthe threshold is crossed, thereby indicating proximity of the medicaldevice to a conductive object, determining a relative distance betweenthe medical device and the conductive object based on one or moredetected values of the energy delivery parameter; (6) comparing therelative distance determined as the device is being advanced todetermine if the distance between the medical device and metal object isdecreasing; and (7) upon determining that the distance between themedical device and the conductive object is decreasing, adjusting aposition of the medical device and repeating steps (3)-(7) until themedical device is positioned at a desired distance from the conductiveobject.
 2. The method of claim 1, wherein the step of adjusting aposition of the medical device comprises moving the medical device awayfrom the conductive object until the value of the energy deliveryparameter no longer exceeds the threshold.
 3. The method of claim 1,wherein the conductive object comprises a secondary medical device andwherein the step of adjusting a position of the medical device comprisesmoving the medical device towards the secondary medical device until themedical device is positioned adjacent the secondary medical device. 4.The method of claim 3, wherein the secondary medical device is selectedfrom the group consisting of a medical guidewire and a snare.
 5. Themethod of claim 1, wherein the threshold is equal to a pre-determinedvalue of the energy delivery parameter.
 6. The method of claim 1,wherein the energy delivery parameter is current.
 7. The method of claim6, wherein the threshold is between about 0.3 Amps to about 1.0 Amps. 8.The method of claim 1, wherein the threshold is equal to a base value,and wherein the method further comprises a step of determining the basevalue by measuring the energy delivery parameter upon advancing themedical device to a target site within the patient's body.
 9. The methodof claim 8, further comprising a step of imaging the medical device,wherein the steps of advancing the medical device and measuring the basevalue are performed concurrently with the step of imaging the medicaldevice.
 10. The method of claim 1, further comprising a step of imagingthe medical device, wherein the step of adjusting a position of themedical device is performed concurrently with the step of imaging themedical device.
 11. The method of claim 9, wherein the step of imagingthe medical device is performed using an imaging modality selected fromthe group consisting of: fluoroscopy, magnetic resonance imaging,computerized tomography scan, electro-anatomical mapping and magneticpositioning system.
 12. The method of claim 10, wherein the step ofimaging the medical device is performed using an imaging modalityselected from the group consisting of: fluoroscopy, magnetic resonanceimaging, computerized tomography scan, electro-anatomical mapping andmagnetic positioning system.
 13. The method of claim 1, furthercomprising a step of providing feedback to a user if the distancebetween the medical device and the conductive object is determined to bedecreasing.
 14. The method of claim 13, wherein the feedback is selectedfrom the group consisting of a visual indication, an electrical controlsignal and an acoustic indication.
 15. The method of claim 14, whereinthe acoustic indication is selected from the group consisting of avolume based acoustic indication and a frequency based acousticindication.
 16. The method of claim 1, wherein the step of adjusting aposition of the medical device is performed automatically.
 17. Themethod of claim 16, wherein the step of adjusting a position of themedical device is performed using an automated navigation system. 18.The method of claim 13, wherein the step of adjusting a position of themedical device is performed automatically using an automated navigationsystem, and wherein the step of providing feedback to the user comprisesproviding an electrical control signal that is receivable by theautomated navigation system.
 19. A method for delivering energy to aregion of tissue within a patient's body using a medical treatmentsystem, the medical treatment system comprising a medical device coupledto an energy delivery source, the method comprising: (1) deliveringenergy from a medical device to material within a patient's body; (2)measuring an energy delivery parameter while the energy is beingdelivered; (3) detecting at least one error if one or more values of theenergy delivery parameter cross a pre-determined threshold; (4) upondetection of at least one error, assessing an extent of the at least oneerror to determine whether the medical device is sufficiently distancedfrom a conductive object to allow for safe delivery of the energy to thematerial within the patient's body; and (5) if the medical device isdetermined to not be sufficiently distanced from the conductive object,adjusting a position of the medical device and repeating steps (2)-(4)until the medical device is sufficiently distanced from the conductiveobject.
 20. The method of claim 19, wherein the energy deliveryparameter is selected from the group consisting of: current, voltage,phase, frequency and impedance.
 21. The method of claim 19, wherein thestep of assessing an extent of the at least one error comprisesquantifying a number of times the energy delivery parameter crosses thethreshold.
 22. The method of claim 19, wherein the step of assessing anextent of the at least one error comprises determining if a collectivemagnitude of the one or more values of the energy delivery parameterexceeds a sensitivity threshold over a predetermined time period
 23. Themethod of claim 22, wherein the sensitivity threshold is fixed.
 24. Themethod of claim 23, wherein the sensitivity threshold is adjustable. 25.The method of claim 19 wherein the step of assessing an extent of the atleast one error comprises determining a duration of time over which theenergy delivery parameter exceeds the threshold.
 26. The method of claim19, wherein the medical device is selected from the group consisting ofa radiofrequency cutting device and a radiofrequency ablation device.27. A method for delivering energy to a region of tissue within apatient's body using a medical treatment system, the medical treatmentsystem comprising a medical device coupled to an energy delivery source,the method comprising the steps of: (1) delivering energy from themedical device to a material within a patient's body; (2) measuring areturn current while the energy is being delivered; (3) detecting if thereturn current exceeds a threshold; (4) if the threshold is exceeded,assessing an extent by which the return current exceeds the threshold todetermine if the medical device is sufficiently distanced from aconductive object; and (5) if the medical device is determined to not besufficiently distanced from the conductive object, adjusting a positionof the medical device and repeating steps (2)-(4) until the medicaldevice is sufficiently distanced from the conductive object.